Cyclohexadiene production



United States Patent 3,294,855 CYCLOHEXADIENE PRODUCTION Lynn H. Slaugh,Pleasant Hill, and John H. Raley, Walnut Creek, Califl, assignors toShell Oil Company, New York, N.Y., a corporation of Delaware No Drawing.Filed Oct. 19, 1964, Ser. No. 404,918 5 Claims. (Cl. 260-666) Thisinvention relates to a process for the partial reduction of aromaticcompounds. More particularly, it relates to a process for the productionof cyclohexadienes by partial reduction of the corresponding aromaticcompounds.

Several methods are available in the art for the partial reduction ofaromatic compounds, e.g., benzene. US. Patent No. 2,182,242, issued May3, 1948, to Wooster, describes a low-temperature reduction of benzene bycontact with sodium in liquid ammonia in the presence of added acidicmaterials such as water and alcohol to produce cyclohexadiene. Such amethod suffers from the disadvantage that the sodium is recovered fromthe reaction system as the hydroxide or alkoxide, forms from which thesodium is not readily recoverable. The resulting effective loss ofsodium precludes the use of such a process on a commercial basis foreconomic reasons. It is also known, see Benkeser, J. Am. Chem. Soc., 77,3230 (1955), that benzene may be partially reduced by reduction withlithium in certain primary amines, such as methylamine land ethylamine,without the addition of added acidic components, but in this process theproducts observed are cyclohexene and cyclohexane. Practical andeconomically feasible methods for the partial reduction of benzene tocyclohexadiene by such procedures have not heretofore been available.

It is an object of the present invention to provide an improved processfor the partial reduction of aromatic hydrocarbons. More particularly,it is an object of the present invention to provide an improved processfor the partial reduction of certain mononuclear aromatic hydrocarbonsto the corresponding 1,4-cyc1ohexadienes. A specific object is toprovide a process for the partial reduction of benzene to1,4-cyclohexadiene.

It has now been found that these objects are accomplished by the processof reacting certain mononuclear aromatic hydrocarbons with lithium insolution in liquid ammonia in the substantial absence of added acidicmaterials. The process of the invention results in the efficientproduction of cyclohexadienes, along with lesser amounts ofcorresponding cyclohexenes, and offers the advantage of providinglithium amide as the metal-containing product from which the elementallithium is readily recoverable, as by pyrolysis of the lithium amide toafford elemental lithium. The utilization of lithium as the metallicreactant appears to be critical as utilization of other alkali metals,sodium for example, does not result in cyclohex-adiene production. I

The aromatic reactants suitably employed in the process of the inventionare mononuclear aromatic hydrocarbons containing a single six-memberedcarbocyclic aromatic ring. Suitable aromatic hydrocarbons contain from 6to 20 carbon atoms and comprise benzene and aliphatichydrocarbyl-substituted benzene. Although the process of the inventionis operable when the central benzene nucleus possesses a plurality ofaliphatic hydrocarbyl substituents, best results are obtained when thecentral benzene nucleus is unsubstituted or possesses from 1 to 2 alkylsubstituents of from 1 to 14 carbon atoms. Preferred aromatic reactantsare therefore characterized as nonto di-alkylbenzene wherein any alkylsubstituent is "ice stance capable of reacting with the lithium underthe con ditions of the reaction to liberate hydrogen. The use of ammoniasubstantially free of hydrolytic agent is highly desirable from .aprocess standpoint, however the presence of small amounts of addedhydrolytic agent, e.g., up to about -1015% by weight, may be toleratedwithout losing the advantages of the invention, but the yield of desiredproduct is decreased by the presence of such materials and in thepreferred modification of the process of the invention, no addedhydrolytic agent is employed.

The ammonia is employed in molar excess over the lithium and thearomatic reactant. Molar ratios of ammonia to the benzene from about 3:1to about :1 are satisfactory, although molar ratios from about 10:1 toabout 50:1 are preferred. The lithium is customarily employed in amountsin excess of the benzene reactant. The probable stoichiometry of thereaction requires utilization of two gram-atoms of lithium per mole ofbenzene reactant. theory, it appears probable that the lithium reactsdirectly with the benzene reactant to produce a mono-metal derivative,e.g., a benzene free-radical anion, which subsequently reacts withammonia to introduce hydrogen into the aromatic ring and form lithiumamide. sequent additional reaction with lithium and ammonia results inthe formation of the observed cyclohexadiene product. Thus, twogram-atoms of lithium are required to effect the desired conversion ofeach mole of benzene reactant. While it appears to be inherent in theprocess of the invention that some lithium will react directly with theammonia to produce hydrogen and lithium amide and thus will not beavailable for utilization in the desired reduction process, amounts oflithium that are less than stoichiometric may be utilized if it is notdesired to effect a high conversion of the benzene reactant. Thus,ratios of gram-atoms of lithium to moles of benzene reactant from about0.25:1 to about 10:1 are suitably employed. Best results are obtainedwhen the ratio of gram-atoms of lithium to moles of benzene is fromabout 1:1 to about 8:1 and ratios from about 2:1 to about 6:1 areparticularly satisfactory.

The partial reduction. process of the invention is conducted at acomparably elevated temperature and pressure and is typically effectedin an autoclave or similar reaction vessel. In contrast with previouslyreported alkali metalammonia reductions which require low temperature,e.g., 40 C., the process of the invention is conducted at temperaturesfrom about 10 C. to about C., although the temperature range from about25 C. to about 80 C. is preferred. The reaction pressure is that whichis sufficient to maintain the ammonia substantially in the liquid phaseduring the reduction process. Pressures from about 2 atmospheres toabout 300 atmospheres are suitable and frequent advantage is taken ofthe pressures generated when the reaction mixture is allowed to reachreaction temperature in a sealed reaction vessel. In the lattermodification the reaction is conducted in an atmosphere of ammonia. Thepresence of other reactive gaseous ma- Without wishing to be bound byany particular A subterials is desirably avoided. It is, on occasion,useful to pressurize the reactor with an inert gas such as argon,helium, methane or the like, prior to or simultaneously with heating thereaction mixture to reaction temperature, although in the preferredmodification of the process of the invention no such inert gas isemployed.

The process of the invention is operable in the presence of inertdiluents, e.g., aliphatic hydrocarbons such as hexane, heptane,cyclohexane, and the like. The presence of such diluents, however,ofliers no advantage to compensate for the increased difiiculty ofproduct separation and in the preferred modification of the invention,no inert diluents are employed. Subsequent to reaction the productmixture is separated and the desired cyclohexadiene product is recoveredby conventional methods such as fractional distillation, selectiveextraction, crystallization and the like. The unreacted ammonia isrecoverable for use in subsequent operations as is any unreacted benzenereactant. A principal advantage of the process of the invention lies inthe fact that the lithium is recovered as the amide regardless of themode of lithium reaction. As previously stated, when lithium amideisobtained as the reaction product, the lithium is easily recoverable, incontrast with prior processes which result in production ofmetal-containing products from which the metal is not readilyregenerated.

The principal products of the process of the invention arecyclohexadienes, although lesser amounts of cyclohexenes are alsoformed. For example, from benzene is obtained 1,4-cyclohexadiene andcyclohexene. Although there exists the possibility of formation of1,3-cyclohexadienes, as well as 1,4-cyclohexadienes, little if any ofthe 1,3-isomer is produced. When the benzene possesses alkylsubstituent(s) position isomers of the alkyl group relative to thedouble bonds present in the ring are observed, e.g., from toluene isobtained a mixture of 1- methyl-1,4-cyclohexadiene andS-methyl-l,4-cyclohexadione, and from p-xylene is obtained a mixture of1,4- dimethylcyclohexadiene and 3,6-dimethylcyclohexadiene.

The cyclohex-adiene products are useful in a variety of applications,particularly as chemical intermediates where they serve as monomers inthe formation of useful copolymers and are additionally suitable forepoxidation to form monoand di-epoxides which are useful as precursorsfor epoxy resins.

To further illustrate the improved process of the invention, thefollowing examples are provided. It should be understood that thedetails thereof are not to be regarded as limitations, as they may bevaried as will be understood by one skilled in this art.

Example I A series of partial reductions of benzene with lithium inammonia was efiected by charging 0.10 mole of benzene, from 2.4 to 2.7moles of liquid ammonia, and varying amounts of lithium to an autoclave.The reactor was sealed and maintained at reaction temperature for theindicated period, after which it was cooled and opened and the productmixture removed therefrom. The organic materials and ammonia wereseparated from the amide by distillation and the product composition wasdetermined by gas-liquid chromatography. The results of this series areshown in T ble I.

TABLE I Product, percent Yield Lithium Temp., Time, G-atoms 0. HoursCyclo- Oyclo 1,4-Cyclohexane hexene hexadicne 53 2. 5 0 2. 6 7. 4 2trace 5. l 30. 7 25 12 0. 5 4. 4 39. 6 60 2 0 5. 2 41. 6 60 8 0 42. 254. 5 0.5 0.2 19. 1 34. 8

The yields in each case are calculated on the basis of benzene charged,and the material not accounted for in the reduced products was unreactedbenzene.

Example II To a reactor was charged 0.1 mole of toluene, 0.4 mole oflithium and 2.6 moles of ammonia. The reactor was sealed and maintainedat 60 C. for 4 hours. The reactor was cooled and opened and the ammoniaand organic materials were separated from the amide by distillation. Theproduct mixture was analyzed by gas-liquid chromatographic methods andwas found to contain a 3.7% yield of methylcyclohexene and a 20.1% yieldof methylcyclohexadiene, each yield being based on the toluene charged.The remaining portion of the product mixture was unreacted benzene.

We claim as our invention:

1. The process of producing a cyclohexadiene product by contacting amononuclear aromatic hydrocarbon of from 6 to 20 carbon atoms, selectedfrom benzene and benzene of from 1 to 2 alkyl substituents, with lithiumand ammonia, in the liquid phase, in the substantial absence ofhydrolytic agent other than ammonia, at a temperature from about 10 C.to about C., in a reaction mixture consisting essentially of saidaromatic hydrocarbon, said lithium and said ammonia.

2. The process of claim 1 wherein the aromatic hydrocarbon is toluene.

3. The process of claim 1 wherein the aromatic hydrocarbon is benzene.

4. The process of claim 1 wherein the ratio of gramatoms of lithium tomoles of said aromatic hydrocarbon is from about 1:1 to about 8:1 andthe molar ratio of said ammonia to said aromatic hydrocarbon is fromabout 3:1 to about 100:1.

A. P. Krapcho et al.: J. Am. Chem. Soc., 81, pp. 3658- 3666, 1959.

J. Benkeser, I. Am. Chem. Soc., 77, pp. 3230-3, 1955.

DELBERT E. GANTZ, Primary Examiner. V. O. KEEFE, Assistant Examiner.

1. THE PROCESS OF PRODUCING A CYCLOHEXADIENE PRODUCT BY CONTACTING AMONONUCLEAR AROMATIC HYDROCARBON OF FROM 6 TO 20 CARBON ATOMS, SELECTEDFROM BENZENE AND BENZENE OF FROM 1 TO 2 ALKYL SUBSTITUENTS, WITH LITHIUMAND AMMONIA, IN THE LIQUID PHASE, IN THE SUBSTANTIAL ABSENCE OFHYDROLYTIC AGENT OTHER THAN AMMONIA, AT A TEMPERATURE FROM ABOUT 10*C.TO ABOUT 135*C., IN A REACTION MIXTURE CONSISTING ESSENTIALLY OF SAIDAROMATIC HYDROCARBON, SAID LITHIUM AND SAID AMMONIA.